1. Technical Field
This invention relates to the technology of producing high density metal powder alloy parts without forging and, more particularly to a process using liquid phase sintering that is dimensionally controllable to achieve a near net shape precision product with high density.
2. Discussion of the Prior Art
High density forming of powder metal is desirable because it increases the mechanical properties of the compacted metal, such as tensile strength, fatigue strength and impact strength. Prior art approaches to high density forming have included: (i) double-press double-sinter with sintering temperatures of 1120.degree.-1200.degree. C., (ii) heated pressing of powders wit a ferro-alloy admixture followed by high temperature sintering, and (iii) high temperature supersolidus sintering of high carbon prealloyed mixtures, such as disclosed in U.S. Pat. No. 5,476,632.
The problem with the double-press double-sinter approach is the high cost of extra processing and multiple equipment costs. The problem with heated pressing (about 300.degree. F.) followed by high temperature sintering is the inability to control the swelling of the resulting metal since high temperature sintering of powders admixed with ferro alloys swells the compact undoing the benefits of heated pressing.
The problem with high temperature supersolidus sintering is the need for post-sintering operations to modify the shape of the carbide network formed during sintering and the need for delicate furnace controls to achieve only grain boundary melting; moreover the resultant compact is hard, containing carbide particles which are abrasive to tools and which present serious machining problems.